Metal-oxide semiconductor (MOS) sensors are normally heated to temperatures of up to 300-400° C. for best sensing. At these temperatures, the material is most reactive. In order to drive off the binder and stabilize the sensor, it is usually necessary to anneal the material to much higher temperatures somewhere in the range of about 900° C. This requires power, which of course increases the costs of production.
When making such MOS devices, MOS materials can be applied to a sensor membrane by a number of techniques such as ink jet printing and screen printing, but stencil printing is preferred because it permits the material to be better formed into a pattern and it maintains the sensing material closer to “bulk” like sensing properties. Using a membrane is more efficient than applying the material to a low conductance substrate, but it does not provide sufficient efficiency for the low power requirements and high temperature required in a range of applications. On the other hand, if the membrane is made more efficient with spiders or legs, the MOS material cannot be stencil printed thereon because the spiders or legs render the membrane less rigid. Alternatively, the MOS device can be made by forming the membrane at the end, but this is difficult because it requires making a device that provides potassium hydroxide (KOH) etch protection or is compatible with reactive ion etch (RIE) instruments.
The art is therefore in need of a novel MOS device and a process of making such a MOS device to address these issues.